1. Field of the Invention
The present invention relates to hydraulic actuators, and more particularly to a hydraulic actuator assembly actuated by an electric motor.
2. Description of the Prior Art
Hydraulic actuators are widely employed in various applications as a source of a pressurized hydraulic fluid. Especially popular are hydraulic actuators driven by an electric motor. These actuators, typically, include a motor driven screw shaft, a non-rotatable nut threaded to the screw shaft, and a hydraulic piston slidably mounted within a hydraulic cylinder and fixed to the nut. When the electric motor is actuated, the rotary motion of the screw shaft is transmitted to the nut that linearly travels along the screw shaft. Since the piston is fixed to the nut, it also moves along the screw shaft, thus generating a desired hydraulic pressure. However, since hydraulic fluid is practically incompressible, the fluctuation of the fluid pressure in a hydraulic system could be extremely large due to even small changes in a volume of the hydraulic cylinder. To cure this problem, hydraulic dampers and/or hydraulic accumulators are, typically, installed in the hydraulic system, increasing the cost and complexity of the hydraulic system.
The present invention provides an improved hydraulic pressure actuator assembly that includes an integral damper/accumulator and a low cost control system.
The hydraulic actuator assembly of the present invention comprises a bi-directional electric motor driving a drive screw shaft through a gear reducer. A shaft coupler is threaded onto the drive screw shaft. The shaft coupler is splined to a stationary coupler retainer to prevent rotational movement thereof. The shaft coupler is connected to a hydraulic piston slidably mounted within a pressure chamber by a compression spring. Thus, when the electric drive motor is actuated by a signal from a control unit, the gear reducer rotates the drive screw. The rotary motion of the drive screw is transmitted to the shaft coupler which travels linearly along the drive screw as the spline fit between the shaft coupler and the coupler retainer prevents the coupler from rotating. The linear axial motion of the shaft coupler is transmitted to the hydraulic piston via the compression spring thereby generating a pressurized hydraulic fluid in a pressure chamber.
The compression spring of the hydraulic actuator functions both as a damper and as accumulator in a hydraulic system to help stabilize hydraulic pressure and to minimize system pressure loss after the motor stops.
An electrical control system for the hydraulic actuator comprises a high-pressure cutoff switch, a low-pressure cutoff switch, and a control switch. The control switch is adapted for activating the hydraulic actuator assembly and selecting the desired operation mode.
Thus, the present invention reduces production cost of the hydraulic system by eliminating separate hydraulic dampers and accumulators and reduces labor cost by eliminating the operation of installing those separate components in the system.